FR2931333A1 - METHODS OF RECEIVING AND TRANSMITTING MULTIMEDIA CONTENT, RECEIVER, TRANSMITTER AND RECORDING MEDIUM, AND SECURITY PROCESSOR THEREFOR - Google Patents

Abstract

This reception method comprises: - whenever a second multimedia content is viewed using an electronic receiver, modifying (114) the value of a counter according to progress instructions associated with this second multimedia content, - storing (114) the value of this counter between non-consecutive visualizations of second multimedia contents interrupted by the visualization of another multimedia content that does not modify the value of the counter, and- the conditioning (118) from viewing a first multimedia content to a sufficient value of the counter.

Description

METHODS FOR RECEIVING AND TRANSMITTING MULTIMEDIA CONTENT, RECEIVER, TRANSMITTER AND RECORDING MEDIUM AND SECURITY PROCESSOR FOR THIS METHOD The invention relates to a method of reception and a method for transmitting a first multimedia content whose visualization is conditioned to the visualization in advance of second multimedia contents. The invention also relates to a receiver, a transmitter, an information recording medium and a security processor for implementing these methods. Multimedia content is content containing audio and / or video. This multimedia content is for example intended to be played on a television set. For example, a multimedia content is a film, an audiovisual program or a music. Such a method of reception is known from the patent application US 2007 294 773 in the name of Microsoft. More specifically, the application of Microsoft describes a method of receiving a first multimedia content, that is to say here a video on demand, and conditioning the descrambling of this video on demand to the visualization at the prior to a second multimedia content, that is to say here advertisements. Video on demand is better known as Video On Demand (VOD). In the Microsoft method, a receiver issues a license to decrypt the video on demand only if all the advertisements have first been viewed. In this way, the visualization of the video on demand is conditioned to the prior visualization of advertisements. In addition, this receiver is equipped with various means to prevent the user from bypassing or zapping advertisements. For example, the receiver is equipped with means for canceling the fast forward.

This known method therefore makes it possible to force viewers to view all the advertisements immediately preceding the video on demand. However, the field of application of this known method is limited to video on demand. Indeed, if this process were transposed to the television broadcast, then a spectator who inadvertently missed the beginning of advertisements that immediately preceded the show he wants to watch, would be deprived of the opportunity to view the show. Such operation is unacceptable for a broadcast television system. The term "broadcast television" refers to the simultaneous broadcasting of the same multimedia content to multiple receivers. Unlike video-on-demand, in broadcast television, the user can not decide when to start streaming media content.

The object of the invention is therefore to propose a method of receiving a first multimedia content whose visualization is conditioned on the prior visualization of second multimedia contents and which can operate in the field of broadcast television.

It therefore has as its object such a method in a context where the second multimedia contents are the only ones to be associated with instructions for progressing the value of the same counter, these progress instructions modifying the whole value of this same counter in the same meaning when executed by an electronic receiver of the first and second multimedia contents. More specifically, this method comprises: - whenever a second multimedia content is viewed using the electronic receiver, the modification of the counter value according to the progression instructions associated with this second multimedia content, - the memorization the value of this counter between non-consecutive visualizations of second multimedia contents interrupted by the visualization of other multimedia content not modifying the value of the counter, and - the conditioning of the complete visualization of the first multimedia content to a predetermined value of the counter.

We assume here that the above method is implemented in the field of television broadcast for a television program that it is desired to pre-condition the display of advertisements. We also assume that the progress instructions increment the counter value when executed by the receiver. In this context, even if the user misses the beginning of the advertisements that immediately precede this television show, he can still be allowed to watch it. Indeed, in the above method, each time the user watches advertisements, the value of the counter is incremented. It is not necessary that the advertisements watched immediately preceding the television show since the value of the counter is memorized. For example, the user can watch a first sequence of advertisements and then change channels to watch a movie. Viewing this movie does not change the counter value. Then some time later, the user looks at another sequence of advertisements which continues to increment the value of the counter. The counter is thus incremented without being reset even if the visualization of the advertisements is interrupted by the visualization of other multimedia contents. Therefore, even before he starts to look at the sequence of advertisements immediately preceding the television program he wants to watch, the value of the counter may already have reached a sufficient value to allow the viewing of this television program. Under these conditions, even if he misses the sequence of advertisements immediately preceding the television show, he is still allowed to watch it. In the above method, it is not necessary for the second multimedia content to immediately precede the first multimedia content. This makes possible the use of this method in the field of broadcast television. Embodiments of this receiving method may include one or more of the following features: prior to viewing each second media content, the method includes clemultiplexing a received multiplexed data stream containing the second multiplexed media content with the instructions progress and the change of the value of the counter is based on progress instructions multiplexed with this second multimedia content; the method comprises selecting the counter whose value must be modified from among several possible counters according to an identifier of this counter associated with the progress instructions; the process comprises; - receiving a group of one or more crypto-periods of the second multimedia content and progress instructions associated with that group, each crypto-period of the second multimedia content being scrambled with a respective control word, and - the changing the value of the counter each time all the crypto-periods of this group are descrambled by the electronic receiver; before a crypto-period of the second multimedia content, the method comprises the reception of a message broadcast simultaneously to all the receivers, capable of receiving the first and second multimedia contents, this message containing a cryptogram CW * of the control word necessary to descramble this crypto-period and progression instructions associated with the group to which this crypto-period belongs; whenever the viewing of the first media content using the electronic receiver is enabled, the method includes changing the counter value in a direction opposite to the progress instructions to condition the viewing of a next first multimedia content. prior viewing of other second additional multimedia contents; the method comprises: - receiving a group of one or more crypto-periods of the first multimedia content and regression instructions of the value of the counter associated with this group, each crypto-period being scrambled with a word of respective control, - whenever all the crypto-periods of the group are descrambled, the change of the value of the counter according to the regression instructions associated with that group in a direction opposite to the progression instructions, and - the prohibition of the descrambling a next group of cryptoperiods of the first multimedia content as soon as the value of the counter reaches a predetermined threshold; the method comprises: - the reception of the first scrambled multimedia content and conditions of access to this first multimedia content, - the prohibition of the descrambling of the first multimedia content if no access title corresponding to the access conditions is registered in the electronic receiver, and on the contrary, - the authorization of the descrambling of the first multimedia content if an access title corresponding to the conditions of access to this first multimedia content is registered in the electronic receiver, and - the inscription in the receiver of an access ticket corresponding to the access conditions as soon as the value of the counter has crossed a predetermined threshold; the method includes limiting the counter value to a predetermined threshold; the method comprises automatically creating the counter in response to receiving instructions for progressing the value of that counter.

The embodiments of the above reception method furthermore have the following advantages: multiplexing the second multimedia contents and progression instructions makes it possible to associate these progress instructions with the second multimedia contents, the use of a counter identifier makes it possible to simultaneously use several counters associated with respective multimedia contents and thus, for example, to condition the display of a third multimedia content to the prior visualization of fourth multimedia contents, the third and fourth multimedia contents being separate and independent of the first and second multimedia contents, - conditioning the change of the value of the counter to descrambling one or more crypto-periods increases the security of the system, - change the value of the counter. in a direction opposite to the progression instructions during each viewing of a first multimedia content makes it possible to condition again the viewing of a next first multimedia content 10 to the preview of second additional multimedia contents, - the modification of the value of the counter as a function of the regression instruction as the first multimedia content is viewed allows a display time of the first multimedia content which is a function of the quantity of second multimedia contents already displayed, - an entry of an access ticket authorizing the complete display of the first multimedia content when a predetermined threshold is reached by the value of the counter allows the display of the first multimedia content for a predetermined duration, 20 - imposing a maximum limit on the value of the counter allows impose an alternation between the visualization of multimedia content conds and first multimedia contents; - Automatically create the counter in response to receiving progress instructions from this. counter avoids having to initialize this counter during the commissioning of the receiver or from specific commands issued by the transmitter. The invention also relates to an information recording medium comprising instructions for executing the above method when these instructions are executed by an electronic computer. The subject of the invention is also a method for transmitting a first multimedia content, the visualization of which is conditioned on the prior visualization of second multimedia contents, in which this method comprises: - issuing instructions for progressing the value of the counter associated with each second multimedia content transmitted, - the transmission between two second multimedia contents of other multimedia contents not associated with instructions for modifying the value of this counter, and - the transmission of conditions of access associated with the first multimedia content transmitted, these access conditions conditioning the complete display of the first multimedia content to a sufficient value of the counter. Embodiments of this transmission method may include the following feature: the method includes issuing counter value regression instructions associated with the first transmitted multimedia content, said regression instructions modifying the value of the same counter in a direction opposite to that of the progress instructions when viewing the first multimedia content is allowed. The subject of the invention is also a receiver of a first multimedia content, the display of which is conditioned on the prior visualization of second multimedia contents and in which the receiver comprises: a memory capable of storing the value of the counter between visualizations non-consecutive second multimedia contents interspersed with the visualization of other multimedia content not modifying the value of the counter, and an electronic calculator capable of: modifying the value of the counter according to the progression instructions associated with the second multimedia contents received each time that a second multimedia content is viewed using this receiver, and • conditioning the complete display of the first multimedia content to a sufficient value of the counter. The invention also relates to a security processor adapted to be implemented in the receiver above. Finally, the subject of the invention is also a transmitter of a first multimedia content, the viewing of which is conditioned on the prior visualization of second multimedia contents, this transmitter being able to: - issue instructions for progressing the value of the counter associated with each second multimedia content transmitted, - to be transmitted, between two second multimedia contents of others, multimedia contents not associated with instructions for progression of the value of this counter, and - to issue access conditions associated with the first content transmitted multimedia, these access conditions conditioning the complete display of the first multimedia content to a sufficient value of the counter. The invention will be better understood on reading the description which will follow given solely by way of non-limiting example and with reference to the drawings in which: FIG. 1 is a schematic illustration of the architecture of a 2 is a schematic illustration of a program schedule 10 used in the system of FIG. 1; FIG. 3 is a schematic illustration of the architecture of a counter used in FIG. FIG. 4 is a flowchart of a method for transmitting and receiving first multimedia contents, the display of which is conditional upon the prior display of second multimedia contents, FIG. illustrai: Schematic ion of the architecture of an ECMcp message used in the system of Figure 1, - Figure 6 is a schematic illustration of an ECMcNP message used in the sys Figure 7 is a diagrammatic illustration of a timing diagram showing the evolution of the value of a meter when the process of Figure 4 is applied, - Figure 8 is a schematic illustration of the architecture. of another embodiment of an ECMcP message, FIG. 9 is a flowchart of another embodiment of a method for transmitting and receiving first multimedia content whose visualization is conditioned by the visualization in advance of other multimedia contents, and - Figure 10 is a schematic illustration of the architecture of an ECMcNP message used in the method of Figure 9. In these figures, the same references are used to designate the same elements. . In the remainder of this description, the features and functions well known to those skilled in the art are not described in detail. In addition, the terminology used is that of conditional access systems to multimedia contents. For more information on this terminology the reader can refer to the following document: Functional Model of Conditional Access EBU Review - Technical European Broadcasting Union, Brussels, BE, No. 266, December 21, 1995.

Figure 1 shows a system 2 for paying broadcast multimedia content. For example, system 2 is a system for broadcasting multiple scrambled TV channels. The descrambling of each of these television channels or groups of television channels is generally conditioned to the payment of a subscription by subscribers. The system 2 comprises at least one transmitter 4 of scrambled multimedia contents and a multitude of receivers able to descramble the multimedia contents broadcast by the transmitter 4. To simplify FIG. 1, only a receiver 6 has been represented. For example, the other receivers are identical to the receiver 6. The transmitter 4 comprises a scrambler 10 able to scramble with a CW control word multimedia content received in clear via a port 12 to as they are received. For this purpose, the scrambler 10 uses the control word contained in a memory 14. The scrambled multimedia content is transmitted to the input of a multiplexer 16. The scrambling of the multimedia content is an encryption operation and the word of control is the encryption key used to scramble the media content. The transmitter 4 also comprises a generator 18 of control words.

The generator 18 regularly modifies the control word contained in the memory 14. The time interval engages two modifications of the control word used to scramble a multimedia content is called crypto-period. A generator 20 generates a new ECM message (Entitlement Control Message) each time the generator 18 generates a new control word. Each ECM message further comprises: a cryptogram CW * of the control word, and access conditions to the scrambled multimedia content. The cryptogram CW * is necessary information, but insufficient in itself, to descramble the multimedia content. For example, the cryptogram CW * is obtained by encrypting the control word with a known operating key of the receiver or a reference to a control word or a cryptogram of the control word contained in the receiver. The access conditions are clestinées to be compared to titles of access or right of access prerecorded in the receiver. The descrambling of the multimedia content is only authorized if the access conditions with which it is associated correspond to prerecorded access titles. For example, an access condition may be a moral level associated with the media content. The ECM message generated by the generator 20 is transmitted to the input of the multiplexer 16.

Here, the generator 20 is connected to a memory 22 containing a grid 24 of the programs. The multiplexer 16 makes it possible to multiplex the scrambled multimedia content with the ECM messages containing the cryptograms CW * necessary for descrambling this multimedia content. The multiplexer 16 thus creates a stream of multiplexed data broadcast to all the receivers via an information transmission network 30. This multiplexing makes it possible to synchronize the transmission of the ECM messages temporally to the transmission of the scrambled multimedia content.

For example, the network 30 is a packet-switched network such as the Internet or a satellite television broadcast network. The receiver 6 comprises a decoder 40 provided with an antenna 42 for receiving the multimedia contents broadcast by the transmitter 4. The decoder 40 also comprises a demultiplexer 44 which demultiplexes the received multiplexed data streams in order to transmit the scrambled multimedia content to a descrambler 46 and the ECM messages to a security processor 48. The processor 48 is detachably connected to the decoder 40. For example, the processor 48 is a smart card. This processor 48 comprises an electronic calculator 50 able to process each ECM message to decrypt the cryptogram CW * and obtain the CW control word for descrambling the multimedia content. The processor 48 is able to transmit to the descrambler 46 the control word CW. The computer 50 is connected to a memory 52 containing instructions for the execution of the method of FIG. 4 when it executes these instructions. In addition, here, this memory 52 includes pre-recorded access titles 54 and several counters. In Figure 1 only a counter 56 has been shown. The structure and use of the other meters is deduced from the description given below in the particular case of the counter 56.

The receiver 6 is connected to a television set 60 own to display the multimedia content descrambled by the decoder 40. Figure 2 shows an example of structure of the grid 24. This grid is here a table containing the following columns: - a column CM-ID intended to contain an identifier of a multimedia content, - a W-ID column intended to contain an identifier of a counter of the receiver 6, - an Nb-TK column intended to contain a number of increment steps of the value of the counter, 40 - a column TK-C intended to contain a number of decrement steps of the current value of the counter, - an I-TK-A column intended to contain the identifier of the counter to be created, and - an A-Max column intended to contain a maximum threshold for the value of the counter.

Increment or decrement steps can also be called points or tokens. This grid 24 therefore makes it possible to associate a multimedia content designated by the identifier of the CM-ID column with a certain amount of information concerning a counter to be incremented, decremented or created in the receivers. FIG. 3 represents an exemplary structure for the counter 56. Here, this counter 56 comprises: a field W-ID intended to contain the identifier of the counter 56; a field TK-A intended to memorize the current value of the counter. 56, an A-Max field intended to contain a maximum threshold for the value of the counter 56, and a field LUD intended to contain the date of the last update of the value of the counter 56. For example, the date is expressed in days, hours, minutes and seconds.

The operation of the system 2 will now be described with reference to the method of FIG. 4 in the particular case where it is sought to condition the display of non-promotional content to the prior visualization of promotional content. For example: - the non-promotional content is a movie or a television show, and - the promotional content is a sequence of advertisements. The system 2 starts with a phase 68 for transmitting the scrambled multimedia contents. Initially, before the broadcast of the multimedia contents, during a step 70, for each promotional or non-promotional multimedia content to be broadcast, the grid 24 is completed from information provided by an operator. More specifically, for each promotional content, the CM-ID, W-ID, Nb-Tk, I-TK-A and A-Max columns are filled in and the TK-C column is empty. For example here, for each promotional content, the CM-ID, W-ID, Nb-TK, I-TK-A and A-Max columns respectively have the following values CP1, C1, 10, 10 and 30. The identifier CP1 is the one associated with each promotional content and the identifier C1 is that of the counter 56. For each non-promotional content, the columns CM-ID, W-ID and TK-C are indicated and the columns Nb-TK, I-TK-A and A-Max are empty. Here, the columns Nb-TK, I-TK-A and A-Max respectively have the following values CNP1, Cl and 1. The identifier CNP1 is the one associated with each non-promotional content. Then during the broadcast of each crypto-period of a multimedia content, during a step 74, the generator 20 creates an ECM message 5 containing: a cryptogram CW * of the control word CW used by the scrambler 14 to scramble the multimedia content during the next crypto-period, - optionally, the access condition (s) necessary (s) to allow the descrambling of this multimedia content, and 10 - possibly instructions for progression or regression of the counter 56 Here an ECM message containing: progress instructions is noted ECMcp. An ECM message containing regression instructions is noted as ECMcNP. An ECM message which does not include a regression instruction or a progress instruction of the counter 56 is noted as ECMN. More specifically, the generator 20 creates an ECMcp message when the multimedia content being broadcast is promotional multimedia content. An example of a possible structure for this ECMcp message is shown in FIG. 5. This ECMcp message contains the following fields: an HD header field of the ECMcp message containing the set of data allowing the exploitation of this message such that for example an operating key index for decrypting the cryptogram CW * and / or a service area identifier concerned in the security processor, - a field CW * containing the cryptogram CW * of the control word CW used to scramble the promotional content, - a field D containing the current date, - an AC zone containing, possibly, one or more conditions for access to the promotional content, 30 - a CU area containing progression instructions, - a WCR area containing instructions the creation of the counter, and - a field S containing a signature of the message ECMcp. Typically, in an ECMcp message there are no access conditions relating to the value of the counter 56. The CU zone comprises: a W-ID field intended to contain the identifier of the counter to be incremented, and a Nb-TK field containing the number of steps to be incremented the value of the counter. For example, the increment step is equal to 1. The WCR zone comprises: an I-TK-A field containing the initial value of the counter to be created, and an A-Max field containing a maximum threshold for the counter to be created. The signature contained in the field S makes it possible to check the integrity of the message ECMcp when it is received. For example, this signature is obtained using a Hash or MAC (Message Authentication Code) applied to the content of the ECMcp message. To complete the value of the fields of the CU and WCR zones, the generator 20 uses the identifier of the multimedia content broadcast and the content of the grid 24. For example, here, the fields W-ID, Nb-TK, I-TK- A and A-Max have, respectively, the following values Cl, 10, 10 and 30. Figure 6 shows an exemplary structure for an ECMcNP message associated with each non-promotional content broadcast. The structure of the ECMcNP message is identical to that of the ECMcp message except that: - it has no CU and WCR zones, and - the AC zone contains an access condition depending on the counter value 56. Here, this access condition is coded using the following fields: an A-CND1 field intended to contain an identifier of the access condition, a W-ID field intended to contain an identifier of the counter. whose value must be verified, and - a TK-C field intended to contain regression instructions of the value of the counter. Here, the regression instruction corresponds to a number of decrement steps from which the current value of the counter must be decreased. The decrement step is chosen equal to 1. As for the ECMcNP message, the values of the fields W-ID and TK-C are obtained using the identifier of the non-promotional content and the contents of the grid 24. Here, the fields W-ID and TK-C contain , Respectively, the values Cl and 1. The AC zone may contain other access conditions. For example, in Figure 6, the first A-CND2 field of a second access condition has been shown. The structure of an ECMN message may either be devoid of fields containing instructions for progression or regression of the value of a counter or may include instructions for progression or regression of the value of a counter different from the counter 56. The structure of the message is therefore deduced from the ECM message structures described above. In parallel with step 74, during a step 82, each crypto-period of the broadcast multimedia content is scrambled using the current CW control word.

Then, in step 84, scrambled media content and associated ECM messages are multiplexed to create the multiplexed data stream. In a step 86, this multiplexed data stream is broadcast by the transmitter 4 through the network 30 to the receivers. Steps 74, 82, 84 and 86 are repeated in loop for each cryptoperiod in order to broadcast the successive crypi: o-periods of the multimedia contents. In parallel, each receiver performs a phase 90 of reception of the scrambled multimedia contents. Initially, in a step 92, the decoder 40 receives and demultiplexes the received multiplexed data stream. The scrambled media content is then sent to the descrambler 46 while the ECM messages are sent to the processor 48. In a step 94, the computer 50 checks the signature S of the received ECM message. In the case where the ECM message is corrupted, the computer 50 proceeds to a step 96 of inhibition of the descrambling of the multimedia content. For example, in step 96, the processor 48 inhibits the decryption of the cryptogram CW * so that descrambling of the multimedia content is made impossible. During step 96, the clear visualization of the multimedia content is therefore not allowed. In the opposite case, during a step 98, the computer 50 compares the access conditions contained in the ECM message received with the access titles 54. In the step 98, the access conditions defined in FIG. help from the TK-C field are not evaluated. In the case where the memory 52 does not include any access title corresponding to these access conditions, then the computer 50 proceeds to step 96. Otherwise, it proceeds to a step 100 of verification of the existence of a counter identifier in the received ECM message. This identifier is searched either in the W-ID field of the CU field or in the W-ID field of the AC field. In the case where the ECM message does not contain any counter identifier, then the display of this multimedia content is not conditioned on the prior visualization of promotional content. For example, it is an ECMN message without CU area and access conditions involving the value of a counter. In this case, it proceeds directly to a step 102 in which the computer 50 decrypts the cryptogram CW * to obtain the control word CW and transmits it to the descrambler 46. Then, the descrambler 46 descrambles the next crypto-period of the content 40 Multimedia received using this control word and transmits the unscrambled multimedia content to the station 60 which displays it in the clear. Thus, viewing of this multimedia content is allowed since the multimedia content is displayed in a form that is directly perceptible and comprehensible for a user. Otherwise, during a step 104, the computer 50 checks whether the counter identifier found in step 100 corresponds to a counter already existing in the memory 52. If not, in a step 106 the calculator 50 checks whether a WCR zone exists in the received ECM message. In the negative, the processor 48 then proceeds directly to step 96. If so, in a step 108, the computer 50 creates in the memory 52 a counter having the structure described with reference to FIG. The values of the W-ID, TK-A, A-Max and LUD fields of the created counter are initialized from the values, respectively, of the W-ID, I-TK-A, A-Max and D fields of the received ECM message. Thus, if the counter 56 did not exist yet during the first reception of non-promotional content, this counter is automatically created during step 108. If the counter corresponding to the identifier contained in the W-ID field already exists in the memory 52 or at the end of the step 108, the computer 50 proceeds to a step 110 of checking the existence of the Nb-TK field in the received ECM message.

If yes, the ECM message received is an ECMcp message. Then, during a step 112, the computer 50 verifies that the date contained in the LUD field of this counter is earlier than the date contained in the D field of the received ECM message. If so, in a step 114, the computer 50 increments the value contained in the TK-A field of this counter 56 by the number of steps indicated in the Nb-TK field of the received ECM message. If necessary, during step 114, the computer 50 limits the incrementation of the value of the counter to not exceed the threshold indicated in the A-Max field. The new value of the counter is then stored until the next iteration of step 114.

In step 114, the field I_UD of the counter 56 is also updated from the date contained in the field D of the received ECM message. At the end of the step 114 or if the last update date of the counter 56 is later than the date contained in the ECM message received, the processor goes directly to the step 102.

In the case where the Nb-TK field does not exist in the received EMC message, it is that this message is an ECMcNP message. The computer 50 then proceeds to a step 116 of verifying the existence of the TK-C field in the AC zone of the received ECM message. If the ECM message received actually contains this field, then this means that the multimedia content currently broadcast is multimedia content whose viewing is conditioned to the prior viewing of other multimedia contents.

In this case, during a step 118, the computer 50 verifies that the current value of the counter identified in step 100 is greater than the value contained in the TK-C field. If not, it is directly proceeded to step 96 which prohibits the display of this multimedia content.

In the opposite case, during a step 120, the computer 50 decrements the current value of the identified counter by a number of steps defined by the value contained in the TK-C field of the received ECM message. In step 120, the date contained in the meter's LUD field is also replaced by the date contained in the received ECM message.

At the end of step 120 or if in step 116, the ECM message does not contain the TK-C field, it is directly proceeded to step 102. FIG. 7 gives an example of the evolution of the value of the counter 56. In FIG. 7, the top band: represents the temporal succession of a non-promotional content 130, a promotional content 131 and a non-promotional content 132. A band 134 represents eight: crypto -periods CP1 to CP8 which cover the time range during which the contents 130 to 132 are received. A band 136 represents the transmission times of the ECM messages.

Here, each ECM message is transmitted to the receiver during the crypto-period that precedes the crypto-period of the multimedia content with which it is associated. Thus, the messages ECM2 to ECM9 are associated, respectively, with the crypto-period CP2 to CP9. The value in brackets represents the value contained in the TK-C field of the ECM message when it is negative or the value contained in the Nb-TK field when this is positive. It can therefore be seen that the messages ECM5 and ECM6 are ECMcp messages associated with the contents 131. The other messages represented are ECMcNP messages. A band 138 represents the value of the TK-A field of the counter 56. A band 140 indicates in gray the crypto-periods during which the visualization of the non-promotional contents is possible and in black the cryptoperiods or such a visualization is not possible. More specifically, during the crypto-period CP1, the value of the counter 56 is equal to 1. Consequently, the descrambling of the multimedia content during the crypto-period CP 2 is authorized because the field TK-C of the message ECM2 is equal to 1. The processing of the message ECM2 during the cryptoperiod CP1 leads to decrementing the value of the counter 56 by 1 so that this value is 0 during the crypto-period CP2. Then, during the crypto-period CP2, the value of the field TK-C of the message ECM3 is compared with the current value of the counter 56. This time, the value of the counter 56 is smaller than the value of the field TK-C . Therefore, descrambling of non-promotional media content is prohibited during the next CP3 crypto-period. In this example, the execution of the method of FIG. 4 also leads to prohibiting the display of the content 130 during the crypto-period CP4. During the crypto-period CP4, the computer 50 receives the message ECM5 in which the value of the field Nb-TK is equal to 10. Therefore, the value of the counter 56 is incremented by 10 and the display of the content 131 is allowed during the crypto-period CP5. During the next crypto-period CP5, another message ECMcp is received so that the value of the counter 56 is incremented by 10 10 again. Then, to descramble the content 132, only ECMcNP messages are received. Thus, the value of the counter 56 is decremented by 1 at the end of each of the crypto periods CP6 and CP7. However, the display of the content 132 is allowed during the crypto-periods CP7 and CP8 because the value of the counter 56 is greater than the value contained in the TK-C field of the ECM7 and ECM8 messages. It is thus clear that the method of FIG. 4 allows a display duration of a non-promotional content which is a function of the duration of promotional contents previewed beforehand. For example, here the allowable viewing time of non-promotional content is directly proportional to the duration of the promotional content viewed. This method therefore encourages users to view the promotional content while leaving great flexibility for the user to accumulate and spend points in his meter. Figure 8 shows another possible embodiment for the structure of an ECMcp message. In this embodiment, the ECMcp message is identical to that described with reference to FIG. 5 except that it does not include the WCR zone. Thus, in this embodiment, counters such as counter 56 must be initialized in memory 52 either during transmission or manufacturing of processor 48 or using EMM (Entitlement Management Message). Another embodiment of the method of FIG. 4 will now be described with reference to FIGS. 9 and 10. The method of FIG. 9 is identical to the method of FIG. 4 with the exception that: step 74, the structure of the ECMcp message created is that shown in Fig. 10, steps 110, 116, 118 and 120 are deleted, and - steps 162 and 164 are introduced after step 114. 40 Message structure ECMcp shown in Fig. 10 is identical to that of the ECMcp message shown in Fig. 5 with the exception that the WCR area is replaced by a RI-C area. The RI-C zone contains instructions for the entry in the memory 52 of a new access ticket if the value of the counter exceeds a predetermined threshold SI. This new access title corresponds to a condition of access to non-promotional content. More precisely, the zone RI-C contains: a field TK-S intended to contain the value of the threshold S1, and an field RI containing the access title to be entered in the memory 52 when the threshold S1 is reached. Preferably, in this embodiment, the ECMcNP message is devoid of regression instructions. Thus, the structure of the ECMcNP message is in no way different from that of a conventional ECM message. After having incremented the value of the counter during the step 114, during the step 162, the calculator 50 checks whether Ila new value of the counter has reached the threshold SI contained in the field TK-S. If it is not, it is directly carried out at step 102. If so, at step 164, the computer 50 registers the access title contained in the RI field in the memory 52. in step 164, the value of the counter 56 is reset. For example, the counter value is reset or decremented by the value Si. Rather than resetting the counter value, it is also possible to increment the value of the threshold S1 by a predetermined step. In this embodiment, each non-promotional content is associated with an A-CND access condition. As long as the memory 52 does not include an access title corresponding to this access condition, viewing the non-promotional content is prohibited. When the value of the counter reaches the threshold S1, then an access title corresponding to this condition A-CND is automatically entered in the memory 52. Therefore the display of the next non-promotional content received is authorized. As in the embodiment of Figure 4, this encourages users to view the promotional content. In addition, the registration of an access ticket makes it possible to precisely adjust the duration of viewable non-promotional content. For example, the new access title stored in the memory 52 allows viewing of the day and the day channel only. Many other embodiments are possible. For example, viewing of non-promotional media content may be prevented by means other than scrambling of that content. In this case, the methods described above can be applied in a context where the first and second multimedia contents are not scrambled. In a variant, the antenna 42 is replaced by a network adapter when the decoder receives the multimedia contents via a cable. For example, the cable is an Ethernet cable.

Here, the counter identifier makes it possible to use and implement the methods of FIGS. 4 and 9 for several different non-promotional multimedia contents so as to subject the display of one of these non-promotional multimedia contents to the value of 'a particular meter.

In a particular embodiment, the counter identifier may be a function of the number of the displayed channel. However, alternatively, a single counter may be used for all non-promotional content. In this case, the identifier of the counter can be omitted.

The methods of Figures 4 and 9 may be modified to allow incrementation of the counter only when a group of several consecutive crypto-periods of the promotional content has been fully visualized. For this purpose, an ECM message includes an indication of the start of a group of cryptoperiods and then a subsequent ECM message broadcast at the end of this crypto-period group includes an end-of-group indication of crypto-periods. In addition, a crypto-period group identifier and a group crypto-period continuity counter are inserted into each ECM message received during this crypto-period group. From this information, the computer 50 verifies that the crypto-periods of this group have all been received immediately one after the other. If yes, the counter value is incremented by the number of steps indicated in the Nb-TK field. If not, that is, if one of the crypto periods has not been descrambled, the counter value remains unchanged. By temporally synchronizing this group of crypto-periods with promotional content, it is possible to encourage the user to view all the promotional content without changing the channel in the middle. Another method for subjecting the incrementation of the counter 56 to the display of an entire segment of promotional content spanning several crypto-periods is to signal the beginning and the end of this group of crypto-periods and to add in each ECM message associated with this group a signature fragment of a local EMM message containing the date, the identifier of the counter and the value of the Nb-TK field to be incremented this counter. Before incrementing the counter corresponding to the identifier contained in this EMM message built locally by the receiver, the computer 50 verifies the signature of this message by comparing it to the signature obtained by concatenating all the signature fragments contained in the messages. ECM messages associated with this group. In the case where the two signatures match, the incrementation of the value of the counter is allowed and otherwise it is prohibited.

In ECM messages, the AC zone may be omitted if the promotional content is freely available.

The progression instructions associated with the promotional contents have been described in the particular case where they correspond to a step of constant increment by cryptoperiod. Thus, the incrementation of the counter is directly proportional to the number of cryptoperiods of promotional content displayed. In a variant, the increment step is not constant and may vary between two cryptoperiods of promotional content. Here, the counter has been described in the particular case where its value is incremented when promotional content is viewed and decremented when non-promotional content is viewed. In another embodiment, the directions for varying the value of this counter are opposite, that is, the counter is decremented when promotional content is viewed and incremented when non-promotional content is viewed. It is possible to replace the operation of incrementing the value of the counter by an operation of incrementing the value of the predetermined threshold beyond which viewing of the non-promotional multimedia content is authorized. The step of increment or decrement is not necessarily an integer. It can be a rational number or a real number.

What has been described in the particular case of the management of encryption keys using ECM and EMM messages applies to any key management method involving the sending of cryptograms of the control word used to transmit the contents. multimedia. The counter is not necessarily stored in the memory of the security processor. For example, alternatively, the counter value is stored in the decoder in encrypted form using a key contained in the security processor. The processor 48 may be immovably integrated in the decoder or in the descrambler. Conversely, the descrambler can be detachable.

What has been described above can also be applied to condition the viewing of non-promotional content to the prior viewing of a given promotional content a number of times. In this case, the value of the counter is, for example, incremented as a function of the number of times that this particular promotional content has been displayed. The ECM structure described and the above methods remain unchanged, only the use of the processes changes. What has been described above also applies in the context of video-on-demand. For example, the above methods can be implemented to condition the free visualization of a video on demand to the visualization in advance of a certain duration of promotional content. In this case, these promotional contents are, for example, those that are played just before the video on demand. The first and second multimedia contents may be different, respectively, from nonpromotional content and promotional content.

For example, the second contents can be first episodes of a television series and the first multimedia contents the last episodes of this series. Thus, users are encouraged to watch all episodes including the first ones. In general, what is described above is not limited to particular types of first and second multimedia contents.

Claims (16)

REVENDICATIONS1. A method of receiving a first multimedia content, the viewing of which is conditional on the prior visualization of second multimedia contents, these second multimedia contents being the only ones to be associated with instructions for progressing the value of the same counter, these instructions progression method modifying the entire value of the same counter in the same direction when they are executed by an electronic receiver of the first and second multimedia contents, characterized in that this method comprises: - whenever a second multimedia content is displayed using the electronic receiver, modifying (114) the value of the counter according to the progression instructions associated with this second multimedia content, - storing (114) the value of this counter between non-consecutive visualizations of seconds multimedia content interspersed with the visualization of other multimedia content not counting the value of the meter, and - the package (118; 98) of the display of the first multimedia content to a predetermined value of the counter. The method of claim 1, wherein prior to viewing each second media content, the method includes demultiplexing (92) a received multiplexed data stream containing the second multiplexed media content with the progress instructions and wherein the modification of the counter value is a function of progression instructions multiplexed with this second multimedia content. 3. Method according to any one of the preceding claims, wherein the method comprises selecting (112) the counter whose value must be modified from among several possible counters according to an identifier of this counter associated with the progress instructions. A method according to any one of the preceding claims, wherein the method comprises: - receiving (92) a group of one or more crypto-periods of the second multimedia content and progression instructions associated therewith each crypto-period of the second multimedia content being scrambled with a respective control word, and - the modification (114) of the counter value each time all the crypto-periods of this group are descrambled by the electronic receiver. 5. Method according to claim 4, wherein before a crypto-period of the second multimedia content, the method comprises receiving (92) a message broadcast simultaneously to all the receivers likely to receive the first and second multimedia contents, this message containing a cryptogram CW * of the control word necessary to descramble this crypto-period and the progression instructions associated with the group to which this crypto-period belongs. A method according to any one of the preceding claims, wherein whenever the display of the first multimedia content using the electronic receiver is enabled, the method comprises modifying (120) the counter value in one direction. opposed to the progress instructions for conditioning the display of a next first multimedia content to the prior viewing of other second additional multimedia contents. The method of claim 6, wherein the method comprises: receiving (92) a group of one or more crypto periods of the first media content and regression instructions of the counter value associated with that group, each crypto-period being scrambled with a respective control word, - each time all the crypto-periods of the group are descrambled, the modification (120) of the value of the counter according to the regression instructions associated with this group in a direction opposite to the progression instructions, and - the prohibition (96) of descrambling a next group of cryptoperiods of the first multimedia content as soon as the value of the counter reaches a predetermined threshold. 8. Method according to any one of the preceding claims, wherein the method comprises: - the reception (92) of the first scrambled multimedia content and conditions of access to this first multimedia content, - the prohibition (98, 96) descrambling the first multimedia content if no access title corresponding to the access conditions is registered in the electronic receiver, and on the contrary, - authorization (98) of the descrambling of the first multimedia content if an access ticket corresponding to the conditions of access to this first multimedia content is registered in the electronic receiver, and - the registration (164) in the receiver of an access ticket corresponding to the access conditions as soon as the value of the counter has crossed. a predetermined threshold. The method of any of the preceding claims, wherein the method includes limiting the counter value to a predetermined threshold. The method of any one of the preceding claims, wherein the method comprises automatically generating (108) the counter in response to receiving instructions for progressing the value of that counter. 11. Information recording medium, characterized in that it comprises instructions for carrying out a reception method according to any one of the preceding claims, when these instructions are executed by an electronic computer. 12. A method for transmitting a first multimedia content, the viewing of which is conditional on the prior visualization of second multimedia contents, these second multimedia contents being the only ones to be associated with instructions for progressing the value of the same counter. an electronic receiver of the first and second multimedia contents, these progress instructions modifying the whole value of the same counter in the same direction when they are executed by the electronic receiver, characterized in that this method comprises: (86) counter value progress instructions associated with each second transmitted multimedia content, - transmitting (86) between two second multimedia contents of other multimedia contents not associated with instructions for modifying the value of that second media content. counter, and - the transmission (86) of access conditions associated with the first multimedia content transmitted, these conditions of access conditioning the complete visualization of the first multimedia content to a sufficient value of the counter. The method of claim 12, wherein the method comprises transmitting (86) regression instructions of the counter value associated with the first transmitted multimedia content, said regression instructions changing the value of the same counter in an opposite direction. to the progression instructions when viewing the first multimedia content is allowed. 14. Receiver of a first multimedia content whose display is conditioned to the prior visualization of second multimedia contents, these second multimedia contents being the only ones to be associated with instructions for progression of the value of the same counter, these instructions progression device modifying the entire value of the same counter in the same direction when they are executed by the electronic receiver of the first and second multimedia contents, characterized in that this receiver comprises: a memory (52) able to store the value of the counter between non-consecutive visualizations of the second multimedia contents interrupted by the visualization of another multimedia content not modifying the value of the counter, and - an electronic calculator (50) able: • to modify the value of the counter according to the instructions of progression associated with the second multimedia content received each time a second co ntenu multimedia is viewed using this receiver, and • condition the full visualization of the first multimedia content to a sufficient value of the counter. Security processor adapted to be implemented in a receiver according to claim 14, characterized in that said security processor comprises an electronic calculator (50) capable of: modifying the value of the counter according to the progress instructions associated with the second multimedia contents received each time a second multimedia content is viewed using this receiver, and • conditioning the complete display of the first multimedia content to a sufficient value of the counter. 16.Submitter of a first multimedia content whose display is conditioned to the prior visualization of second multimedia contents, these second multimedia contents being the only ones to be associated with instructions for progressing the value of the same counter of a electronic receiver of the first and second multimedia contents, these progress instructions modifying the entire value of the same counter in the same direction when they are executed by the electronic receiver, characterized in that the transmitter (4) is capable of: issuing counter value progress instructions associated with each second multimedia content transmitted, - transmitting, between two second multimedia contents of others, multimedia contents not associated with instructions for progressing the value of this counter, and - at to issue access conditions associated with the first multimedia content 5 transmitted, these access conditions conditioning the complete visualization of the first multimedia content to a sufficient value of the counter.